To respond to miniaturization of a semiconductor device such as an LSI, optical lithography by a phase sift mask (PSM) is used. The PSM uses interference of light to enable exposure with resolution higher than that defined by wavelength of light.
Here, in a Levenson phase shift mask, for example, a pattern is created in a light shielding film formed on a light transmissive mask substrate as a first layer, and then a pattern for a shifter on the mask substrate as a second layer. Therefore, before drawing of the pattern of the second layer, alignment with the pattern of the first layer is performed. For the alignment, a secondary electron image of the pattern (alignment mark) of the first layer is used.
However, in recent years, the light shielding film significantly becomes thinner and therefore detection of the alignment mark becomes more difficult, so that it becomes more difficult to secure the accuracy of overlapping the patterns of the first layer and the second layer.
Note that a technology for obtaining a sufficient detection signal of the alignment mark is disclosed.